Package org.apache.druid.segment.loading

Class AcquireSegmentAction

java.lang.Object

org.apache.druid.segment.loading.AcquireSegmentAction

All Implemented Interfaces:

Closeable, AutoCloseable

public class AcquireSegmentAction
extends Object
implements Closeable

This class represents an intent to acquire a reference to a Segment and then use it to do stuff, and finally closing when done.

When an AcquireSegmentAction is created, segment cache implementations will create a 'hold' to ensure it cannot be removed from the cache until this action has been closed.

Calling getSegmentFuture() is what actually initiates the 'action', and will return a segment reference provider if already cached, or attempt to download from deep storage to load into the cache if not. The Segment returned by acquiring a reference from the ReferenceCountedObjectProvider returned by the future places a separate hold on the cache until the segment itself is closed, and MUST be closed when the caller is finished doing segment things with it.

The caller must also call close() on this object to clean up the hold that exists while possibly loading the segment, and may do so as soon as the Segment is acquired (or can do so earlier to abort the load and release the hold).

Constructor Summary

Constructors

Constructor	Description
AcquireSegmentAction(Supplier<com.google.common.util.concurrent.ListenableFuture<AcquireSegmentResult>> segmentFutureSupplier, Closeable loadCleanup)

Method Summary

Modifier and Type	Method	Description
void	close()
com.google.common.util.concurrent.ListenableFuture<AcquireSegmentResult>	getSegmentFuture()	Get a ReferenceCountedObjectProvider<Segment> to acquire a reference to an item that exists in the cache, or if necessary/possible, fetching it from deep storage.
static AcquireSegmentAction	missingSegment()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

AcquireSegmentAction

public AcquireSegmentAction(Supplier<com.google.common.util.concurrent.ListenableFuture<AcquireSegmentResult>> segmentFutureSupplier,
 @Nullable
 Closeable loadCleanup)

Method Details

missingSegment

public static AcquireSegmentAction missingSegment()

getSegmentFuture

public com.google.common.util.concurrent.ListenableFuture<AcquireSegmentResult> getSegmentFuture()

Get a ReferenceCountedObjectProvider<Segment> to acquire a reference to an item that exists in the cache, or if necessary/possible, fetching it from deep storage. This is typically ReferenceCountedSegmentProvider, either as an immediate future if the segment already exists in cache. The 'action' to fetch the segment and return the reference provider is not initiated until this method is called.

close

public void close()
           throws IOException

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Throws:

IOException